Antenna device and communication terminal apparatus

ABSTRACT

An antenna device includes a feed coil connected to a feed circuit, and a coil antenna disposed near the feed coil. A ferrite sheet, in which a magnetic loss term in a usable frequency band is relatively large, is provided between the feed coil and the coil antenna. The feed coil and the coil antenna are magnetically coupled to each other via the ferrite sheet. With this configuration, signal transmission efficiency between the feed coil and the coil antenna is enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to antenna devices and communicationterminal apparatuses. In particular, the present invention relates to anantenna device preferably for use in an RFID tag or a reader/writer thatoperates in an HF band, and a communication terminal apparatus includingthe antenna device.

2. Description of the Related Art

RFID (Radio Frequency Identification) systems are widely used as billingsystems or article management systems. In an RFID system, areader/writer and an RFID tag are caused to perform wirelesscommunication in a noncontact manner, and radio-frequency signals aretransmitted and received between these devices. The reader/writer andthe RFID tag each include an RFID IC chip for processing radio-frequencysignals and an antenna for transmitting and receiving radio-frequencysignals. A coil antenna is used as an antenna in the case of, forexample, an HF-band RFID system utilizing a 13.56 MHz band. The coilantenna on the reader/writer side and the coil antenna on the tag sideare coupled to each other via an induction magnetic field.

In recent years, HF-band RFID systems have been utilized forcommunication terminal apparatuses such as mobile phones, and thecommunication terminal apparatuses have been used as readers/writers orRFID tags in some cases. In these cases, an RFID IC chip is mounted on aprinted wiring board, and an antenna is adhered to a terminal housing oris provided in a free space in the terminal housing. Thus, the RFID ICchip and the antenna are connected to each other in a direct-currentmanner via a flexible cable or a contact pin.

On the other hand, as disclosed in, for example, Japanese Patent No.4325621, a configuration is known in which a feed coil connected to anRFID IC chip is mounted on a control board, and the feed coil ismagnetically coupled to a coil antenna provided on an antenna board.With this configuration, a radio-frequency signal can be transmittedfrom the feed coil to the coil antenna via a magnetic field, and thusthe RFID IC chip and the coil antenna can be connected to each otherwithout using a flexible cable or a contact pin.

As in the antenna device disclosed in Japanese Patent No. 4325621, in acase where a feed coil and a coil antenna are magnetically coupled toeach other and signals are transmitted accordingly, a mutual inductanceis generated between the feed coil and the coil antenna, and thus theimpedances or resonance frequencies may be different from each otherinconveniently, depending on the positional relationship therebetween.In particular, if the feed coil and the coil antenna are directly andmagnetically coupled to each other and if the degree of coupling isextremely high, the resonance points of the feed coil and the coilantenna are separated from each other even if the resonance frequenciesof the feed coil and the coil antenna correspond to a carrier frequency.Thus, the signal transmission efficiency from the feed coil to the coilantenna, or the signal transmission efficiency from the coil antenna tothe feed coil decreases, and as a result, the communication distancedecreases.

SUMMARY OF THE INVENTION

In view of the above-described circumstances, preferred embodiments ofthe present invention provide an antenna device in which a signaltransmission efficiency between a feed coil and a coil antenna is highand a communication distance is long, and a communication terminalapparatus including the antenna device.

An antenna device according to a preferred embodiment of the presentinvention is an antenna device including a feed coil connected to a feedcircuit, and a coil antenna disposed near the feed coil. A magneticlayer is provided between the feed coil and the coil antenna. A productof a relative permeability of a magnetic material of the magnetic layerand a thickness (units of millimeters) of the magnetic layer is lessthan twenty. The feed coil and the coil antenna are magnetically coupledto each other via the magnetic layer.

A communication terminal apparatus according to another preferredembodiment of the present invention is a communication terminalapparatus including a housing, a feed circuit provided in the housing, afeed coil connected to the feed circuit, and a coil antenna disposednear the feed coil. A magnetic layer is provided between the feed coiland the coil antenna, and the feed coil and the coil antenna areelectromagnetically coupled to each other via the magnetic layer.

According to various preferred embodiments of the present invention, afeed coil and a coil antenna are magnetically coupled to each other viaa magnetic layer that has an appropriately determined permeability andthickness. Thus, the degree of coupling between the feed coil and thecoil antenna can be maintained within an appropriate range. Accordingly,an antenna device having enhanced signal transmission efficiency and anincreased communication distance, and a communication terminal apparatusincluding the antenna device are provided.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic perspective view of an antenna device 101according to a first preferred embodiment of the present invention, andFIG. 1B is a schematic cross-sectional view of a communication terminalapparatus (a mobile communication terminal such as a mobile phoneterminal) including the antenna device 101.

FIG. 2A is a front view of the antenna device 101, and FIG. 2B is apartial plan view of the antenna device 101.

FIG. 3 is an exploded perspective view of a feed coil 10.

FIG. 4 is an exploded perspective view of a coil antenna 20 and aferrite sheet 30.

FIG. 5A is an equivalent circuit diagram illustrating a state where afeed circuit 9 is connected to the antenna device 101. FIG. 5B is adiagram illustrating an induction magnetic field that is formed betweenthe coil antenna 20 and an antenna on the communication partner side.

FIG. 6A and FIG. 6B are diagrams each illustrating an induction magneticfield of an antenna device which is a target compared to the antennadevice according to a preferred embodiment of the present invention.

FIGS. 7A-7D are diagrams illustrating changes in resonance frequenciesof the coil antenna and the feed coil in a case where the thickness ofthe ferrite sheet 30 is changed.

FIG. 8A is a schematic perspective view of an antenna device 102according to a second preferred embodiment of the present invention, andFIG. 8B is a front view of the antenna device 102.

FIG. 9A is a schematic perspective view of an antenna device 103according to a third preferred embodiment of the present invention, andFIG. 9B is a partial plan view of the antenna device 103.

FIG. 10A is a schematic cross-sectional view of a communication terminalapparatus 203 including the antenna device 103. FIG. 10B is a plan viewof the antenna device 103 included in the communication terminalapparatus 203.

FIG. 11A is a schematic perspective view of an antenna device 104according to a fourth preferred embodiment of the present invention, andFIG. 11B is a front view of the antenna device 104.

FIG. 12A is a schematic perspective view of an antenna device 105Aaccording to a fifth preferred embodiment of the present invention, FIG.12B is a schematic perspective view of an antenna device 105B accordingto the fifth preferred embodiment of the present invention, and FIG. 12Cis a partial plan view of the antenna devices 105A and 105B.

FIG. 13 is a partial plan view of a communication terminal apparatus 206including an antenna device according to a sixth preferred embodiment ofthe present invention.

FIG. 14A is a schematic perspective view of an antenna device 107according to a seventh preferred embodiment of the present invention,and FIG. 14B is a front view of the antenna device 107.

FIGS. 15A-15C are diagrams each illustrating the angle formed by acommunication terminal apparatus 207 including the antenna device 107and a coil antenna on the communication partner side.

FIG. 16A is a plan view of an antenna device 108 according to an eighthpreferred embodiment of the present invention, FIG. 16B is a partialplan view thereof, and FIG. 16C is a cross-sectional view taken along aC-C portion of FIG. 16B.

FIG. 17A is a diagram illustrating the induction magnetic field of theantenna device in a case where the permeability of the ferrite sheet 30(magnetic layer) is high, or in a case where the thickness of theferrite sheet 30 is large, and FIG. 17B is a diagram illustrating theinduction magnetic field of the antenna device in a case where thepermeability of the ferrite sheet 30 (magnetic layer) is low, or in acase where the thickness of the ferrite sheet 30 is small.

FIG. 18A is a diagram illustrating the relationship between the productof the relative permeability (real part permeability μ′) and thethickness of the ferrite sheet 30 of an antenna device according to aninth preferred embodiment of the present invention and the maximumcommunication distance, and FIG. 18B is a diagram illustrating thevalues thereof.

FIG. 19A is a perspective view of the coil antenna 20 of an antennadevice according to a tenth preferred embodiment of the presentinvention, and FIG. 19B is an exploded perspective view thereof.

FIG. 20A is a plan view of the coil antenna 20, and FIG. 20B is anequivalent circuit diagram of the coil antenna 20.

FIG. 21A and FIG. 21B are plan views of a coil antenna according to aneleventh preferred embodiment of the present invention.

FIG. 22A includes a plan view and a front view of an antenna deviceaccording to a twelfth preferred embodiment of the present invention,and FIG. 22B is a diagram illustrating the relationship between themaximum communication distance and a dimension Y from an end portion ofthe ferrite sheet 30 to one end of the feed coil 10.

FIGS. 23A and 23B are front views of the antenna device according to thetwelfth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An antenna device according to various preferred embodiments of thepresent invention is an antenna device preferably for use in an HF-bandRFID system or the like, and includes a feed coil connected to a feedcircuit, and a coil antenna disposed near the feed coil. A communicationterminal apparatus according to other preferred embodiments of thepresent invention is a communication terminal apparatus including theforegoing antenna device, and includes a feed circuit provided in ahousing, a feed coil connected to the feed circuit, and a coil antennadisposed near the feed coil. In the antenna device and the communicationterminal apparatus, a magnetic layer such as a ferrite sheet is disposedbetween the feed coil and the coil antenna. The feed coil and the coilantenna are magnetically coupled to each other via the magnetic layer.

As described above, the feed coil and the coil antenna are magneticallycoupled to each other via the magnetic layer. The magnetic layer isdefined so that the product of the relative permeability of the magneticmaterial of the magnetic layer and the thickness (units of millimeters)of the magnetic layer is less than twenty. Accordingly, even in a casewhere the feed coil and the coil antenna are disposed close to eachother, the degree of coupling (coupling efficiency) does not becomeextremely high and can be maintained within an appropriate range. Thisprevents a situation from occurring where the resonance points of thefeed coil and the coil antenna are significantly separated from eachother. Accordingly, a compact antenna device and communication terminalapparatus can be provided in which impedance matching is achievedbetween the feed circuit and the antenna device, the transmissionefficiency of a radio-frequency signal is high, and the communicationdistance is long.

Here, the magnetic layer does not completely and magnetically shield thefeed coil and the coil antenna, and allows part of magnetic-fieldcomponents in a carrier frequency to be transmitted therethrough. Thus,in a case where a magnetic layer having a large permeability is used,such as a ferrite sintered body, the thickness of the magnetic layer ispreferably small because it is necessary to allow the feed coil and thecoil antenna to be magnetically coupled to each other via the magneticlayer. Specifically, the product of the relative permeability and thethickness of the magnetic layer (units of millimeters) is preferably setto be less than twenty. Preferably, the thickness of the magnetic layeris about 300 μm or less, for example. If the thickness is more thanabout 300 μm, it is difficult that the product of the relativepermeability and the thickness of the magnetic layer (units ofmillimeters) is less than twenty. In addition, a large thicknessinhibits a decrease in size of the antenna device.

In various preferred embodiments of the present invention, the feedcircuit is a functional circuit that generates a radio-frequency signaland supplies the radio-frequency signal to the coil antenna. In an RFIDsystem, for example, an RFID IC chip corresponds to the feed circuit.The RFID IC chip is a semiconductor integrated circuit including an RFcircuit, a memory circuit, a logic circuit, and so forth. The RFID ICchip preferably is a silicon semiconductor element or a GaAssemiconductor element, for example. The semiconductor element may be abare chip IC or a package IC, for example.

The feed coil includes a coil pattern connected to the feed circuit. Thecoil pattern is constituted by at least one coil conductor. The coilpattern may be defined by a coil conductor that is wound through aplurality of turns, or only one turn. Alternatively, the coil patternmay be a multilayer coil pattern defined by connecting a plurality oflayers of a coil conductor. Alternatively, the feed coil may include amagnetic core constituted by a ferrite sintered body or the like. Whentransmitting a radio-frequency signal, the feed coil transmits theradio-frequency signal to the coil antenna via a magnetic field. Whenreceiving a radio-frequency signal, the feed coil receives theradio-frequency signal from the coil antenna via a magnetic field.

It is not always necessary that the feed coil and the coil antennaoverlap each other, and the feed coil and the coil antenna may bedisposed close to each other, in plan view in the direction of thewinding axis of the coil antenna. However, it is preferable that one ofend portions of the feed coil overlap the outside of the magnetic layer,and that the other end portion overlap the inside of the magnetic layer.

Further, it is preferable that the feed coil be disposed such that thewinding axis thereof crosses the winding axis of the coil antenna. Morespecifically, it is preferable that the feed coil be disposed such thatthe winding axis of the feed coil is perpendicular or substantiallyperpendicular to the winding axis of the coil antenna. In particular, ina case where the feed coil is disposed such that at least a portion ofthe feed coil overlaps a coil conductor constituting the coil antenna,it is preferable that the feed coil be disposed such that the windingaxis of the coil antenna is perpendicular or substantially perpendicularto the winding axis of the feed coil in plan view in the direction ofthe winding axis of the coil antenna. This is because the degree ofcoupling between the feed coil and the coil antenna with respect tochange in the distance therebetween is stabilized.

Further, it is preferable that the feed coil have an inductance valuethat enables the feed coil and the feed circuit to form a resonancecircuit having a resonance frequency corresponding to a carrierfrequency. That is, in a case where the feed circuit is an IC chip, itis preferable that the capacitance of the IC chip and the inductance ofthe feed coil define an LC parallel resonance circuit, and that theresonance frequency thereof be a frequency corresponding to the carrierfrequency of a communication signal. In a case where the feed circuitand the feed coil define a resonance circuit that resonates at thecarrier frequency, the resonance frequency of the antenna device iseasily designed.

In a case where the housing of the communication terminal apparatusincludes a principal surface and an end surface connected to an endportion of the principal surface, it is preferable that the feed coil bedisposed in the housing near an end portion of the housing such that thewinding axis of the feed coil is perpendicular or substantiallyperpendicular to the end surface of the housing. With this disposition,a magnetic flux easily passes through a coil opening of the feed coil,and the communication distance is increased.

The coil antenna is disposed near the feed coil, and is constituted byat least one coil conductor. The coil conductor may be wound through aplurality of turns, or may include a plurality of layers. Preferably,the coil antenna is a planar coil that includes a first principalsurface and a second principal surface. In a case where the coil antennais a planar coil, the coil antenna can be provided in a small spacebetween the housing and various components provided in the housing. Thesurfaces of the planar coil may include a plurality of flat surfaces.

In a case where the first principal surface of the planar coil faces anantenna of the communication partner, it is preferable that a magneticlayer be arranged so as to cover the second principal surface. Normally,communication terminal apparatuses such as mobile phones are providedwith a metal body having a relatively large area (corresponding to a“conductive layer”), such as a ground conductor of a printed wiringboard or a metal cover of a battery. If the coil antenna is disposednear such a metal body, an eddy current flows through the metal body tocancel a change in the magnetic flux generated by the coil antenna.Accordingly, an energy loss (an eddy current loss) increases, and it maybecome impossible to ensure a sufficient communication distance.Therefore, a magnetic layer is provided between the second principalsurface of the planar coil and the metal body, so that the degree ofcoupling between the planar coil and the feed coil can be controlled,and a decrease in communication distance caused by an eddy current losscan be prevented.

Preferably, the coil antenna is a resonance circuit having a resonancefrequency corresponding to the carrier frequency of a communicationsignal. For example, the coil antenna may be constituted by an LCparallel resonance circuit including a coil conductor having a certaininductance and a chip capacitor having a certain capacitance.Alternatively, a first coil conductor and a second coil conductor may beoverlapped with each other with an insulating layer therebetween so thatthe directions of currents flowing through these conductors are thesame, and an LC parallel resonance circuit may be constituted byinductances of the individual coil conductors and a stray capacitancegenerated between the coil conductors. The coil antenna may also bereferred to as a booster antenna, and thus need not always have aresonance frequency corresponding to the carrier frequency of acommunication signal. However, if the coil antenna resonates at afrequency corresponding to the carrier frequency, an energy lossdecreases, and the communication distance increases.

The coil antenna need not be a planar coil having only one flat surface,and may be a planar coil having at least, for example, a first flatsurface and a second flat surface which is connected to the first flatsurface. In this case, it is preferable that the feed coil be disposedin a region surrounded by the first flat surface and the second flatsurface. In particular, in a case where the housing of the communicationterminal apparatus includes a principal surface and an end portion (endsurface), it is preferable that the first flat surface be parallel orsubstantially parallel with the principal surface of the housing andthat the second flat surface extend along the end portion (end surface)of the housing to form an angle with the first flat surface. With thisconfiguration, the directivity of the antenna device is increased, and afavorable communication state is ensured between the communicationterminal apparatus and an apparatus on the communication partner sideeven if the communication terminal apparatus faces the antenna on thecommunication partner side in various directions.

A desirable preferred embodiment of the present invention has beendescribed above. The antenna device and the communication terminalapparatus according to the present invention are not limited to those ofthe above-described preferred embodiment. For example, the antennadevice according to the present invention is not limited to an antennadevice for an HF-band RFID system, and may be used for various frequencybands and various communication systems, such as a UHF-bandcommunication system. In the case of using the antenna device as anantenna for an RFID system, the antenna device may be used as an antennafor a reader/writer or an antenna for an RFID tag.

First Preferred Embodiment

An antenna device and a communication terminal apparatus 201 accordingto a first preferred embodiment are an antenna device for an HF-bandRFID system utilizing a carrier frequency of 13.56 MHz, and a mobilecommunication terminal including the antenna device mounted therein.FIG. 1A is a schematic perspective view of an antenna device 101according to the first preferred embodiment, and FIG. 1B is a schematiccross-sectional view of a communication terminal apparatus (a mobilecommunication terminal such as a mobile phone terminal) including theantenna device. FIG. 2A is a front view of the antenna device 101, andFIG. 2B is a partial plan view of the antenna device 101.

As illustrated in FIG. 1A and FIG. 2A, the antenna device 101 includes afeed coil 10 connected to a feed circuit, a coil antenna 20 disposednear the feed coil 10, and a ferrite sheet 30 provided between the feedcoil 10 and the coil antenna 20. In this preferred embodiment, theantenna device 101 further includes a printed wiring board 50. The feedcoil 10 is mounted on the printed wiring board 50. The feed coil 10includes a magnetic core 11 and a coil pattern 12 located on themagnetic core 11. The specific configuration will be described below.

The ferrite sheet 30 preferably has a relative permeability of 50 and athickness of about 0.3 mm, for example. The product of the relativepermeability and the thickness preferably is 15 (less than 20), forexample.

As illustrated in FIG. 2A, the coil antenna 20 includes a base sheet 21,a coil conductor 22 a located on the upper surface of the base sheet 21,and a coil conductor 22 b located on the lower surface of the base sheet21.

As illustrated in FIG. 1B, the communication terminal apparatus 201includes a terminal housing 60, which is rectangular or substantiallyrectangular parallelepiped shaped. The antenna device 101 is provided inthe terminal housing 60. An RFID IC chip 90 and the feed coil 10 aredisposed near an end portion of the printed wiring board 50. The RFID ICchip 90 is connected to the feed coil 10.

On an inner surface on a back surface LF side of the terminal housing60, the coil antenna 20 is adhered via a binder 40, such as adouble-sided adhesive sheet.

The printed wiring board 50 preferably is made of a thermosetting resin,such as epoxy resin, and the planar shape thereof preferably isrectangular or substantially rectangular. The printed wiring board 50includes a substrate 51 and various conductive patterns. A groundconductor 52, which preferably has the same or substantially the sameshape as the planar shape of the printed wiring board 50, is provided inan inner layer of the substrate 51. The ground conductor 52 functions asa ground electrode of various electronic components (not illustrated)included in the communication terminal, such as a radio-frequencycircuit, a power supply circuit, and a liquid crystal driving circuit.

FIG. 3 is an exploded perspective view of the feed coil 10. The feedcoil 10 includes a magnetic core including a ferrite sintered body, anda coil pattern wound around the magnetic core. Specifically, asillustrated in FIG. 3, the magnetic core includes a magnetic layer 112 aand a magnetic layer 112 b. The base body of the feed coil 10 has amultilayer structure in which the magnetic layers 112 a and 112 b aresandwiched between non-magnetic layers 111 a and 111 b. An in-planeconductor 121 a, which is a portion of the coil pattern, is provided onthe non-magnetic layer 111 a. An in-plane conductor 121 b, which is aportion of the coil pattern, is located on the magnetic layer 112 b.End-surface conductors 122 a and 122 b, each being a portion of the coilpattern, are provided on both end surfaces of the magnetic layers 112 aand 112 b. Input/output terminals 123 a and 123 b are provided on thelower surface of the non-magnetic layer 111 a. Via-hole conductors thatelectrically connect the in-plane conductor 121 a and the input/outputterminals 123 a and 123 b are provided on the non-magnetic layer 111 a.The end-surface conductors 122 a and 122 b correspond to half of athrough-hole conductor or a via-hole conductor having an inner surfaceon which a conductive film is formed in the state of a motherboard.

As described above, the in-plane conductors 121 a and 121 b and theend-surface conductors 122 a and 122 b define the coil pattern of thefeed coil 10.

The magnetic layers 112 a and 112 b, and the non-magnetic layers 111 aand 111 b preferably are ferrite ceramic sintered layers. The in-planeconductors 121 a and 121 b, and the end-surface conductors (through-holeconductor, via-hole conductor) 122 a and 122 b preferably are sinteredbodies of a conductive material mainly containing silver, copper, or thelike printed on or filled in a ceramic green sheet, which is a precursorof a ceramic sintered layer.

As described above, the feed coil 10 preferably is a chip componentincluding a multilayer structure serving as a base body, and is mountedon the surface of the printed wiring board 50 via the input/outputterminals 123 a and 123 b. As illustrated in FIG. 2B, the feed coil 10is mounted on the surface of the printed wiring board 50 such that thecoil pattern of the feed coil 10 overlaps the coil conductorsconstituting the coil antenna 20 in plan view in the direction of thewinding axis of the coil antenna 20.

FIG. 4 is an exploded perspective view of the coil antenna 20 and theferrite sheet 30. The coil antenna 20 is constituted by the base sheet21, which is preferably made of PET or the like, the coil conductor 22 alocated on the upper surface of the base sheet 21, and the coilconductor 22 b located on the lower surface of the base sheet 21. Thecoil conductors 22 a and 22 b are thin metal films, such as copper foilor aluminum foils. In this preferred embodiment, the coil antenna is aplanar coil constituted by the base sheet 21 and the coil conductors 22a and 22 b. In FIG. 4, the surface on the upper side is a firstprincipal surface oriented toward an antenna on the communicationpartner side, and the surface on the lower side is a second principalsurface opposite thereto.

The coil conductor 22 a and the coil conductor 22 b are patterns thatare wound so that, when currents flow from one ends of the respectivecoil conductors toward the other ends, the directions in which thecurrents flow in the respective coil conductors are the same. The coilconductors 22 a and 22 b are disposed such that at least portions of thecoil conductors 22 a and 22 b overlap each other in plan view in thedirection of the winding axes thereof. As a result, these coilconductors 22 a and 22 b are coupled to each other via a capacitance.

As illustrated in FIG. 1B, the ferrite sheet 30 is provided between thecoil antenna 20 and the ground conductor 52, and also between the coilantenna 20 and the feed coil 10. The feed coil 10 and the coil antenna20 are disposed such that the winding axis of the feed coil 10 isperpendicular or substantially perpendicular to the winding axis of thecoil antenna 20, that the feed coil 10 and the coil antenna 20 partiallyoverlap each other in plan view of the coil antenna 20, and that twoopening portions (both end portions) of the feed coil 10 protrude from aregion where the conductors of the coil antenna 20 are provided. Withsuch disposition, the degree of coupling between the feed coil 10 andthe coil antenna 20 increases, and stable communication characteristicsare obtained even if the distance between the coil antenna 20 and thefeed coil 10 increases.

FIG. 5A is an equivalent circuit diagram illustrating a state where afeed circuit 9 is connected to the antenna device 101. On a feed sideincluding the feed circuit 9 and the feed coil 10, a capacitance Ccomposed of a stray capacitance of the RFID IC chip and a matchingcapacitor, and an inductance L of the feed coil 10 define an LC parallelresonance circuit. The resonance frequency of the LC parallel resonancecircuit is set to be equal or substantially equal to the carrierfrequency of a communication signal (13.56 MHz). On an antenna sideincluding the coil antenna 20, an inductance L1 of the coil conductor 22a, an inductance L2 of the coil conductor 22 b, and capacitances C1 andC2 generated between the coil conductor 22 a and the coil conductor 22 bdefine an LC parallel resonance circuit. The resonance frequency of theLC parallel resonance circuit is set to be equal or substantially equalto the carrier frequency of a communication signal (13.56 MHz). The feedcoil 10 and the coil antenna 20 are magnetically coupled to each othervia the ferrite sheet 30. That is, the feed coil 10 and the coil antennaare magnetically coupled to each other by a weak mutual inductance viathe ferrite sheet 30.

FIG. 5B is a diagram illustrating an induction magnetic field that isgenerated between the coil antenna 20 and an antenna on thecommunication partner side (not illustrated). The major portion of theinduction magnetic field that is generated between the coil antenna 20and the antenna on the communication partner side is induced along anupper-side interface of the ferrite sheet 30, as represented by amagnetic flux φa. A portion of the induction magnetic field is inducedto the feed coil 10 via the ferrite sheet 30, as represented by amagnetic flux φb. Since the ferrite sheet 30 exists between the coilantenna 20 and the ground conductor 52, the occurrence of an eddycurrent in the ground conductor 52 caused by the induction magneticfield of the current flowing through the coil antenna 20 is minimized orprevented.

FIG. 6A and FIG. 6B are diagrams each illustrating an induction magneticfield of an antenna device which is a target compared to the antennadevice according to a preferred embodiment of the present invention.FIG. 6A illustrates an example of an antenna device not including aferrite sheet, and FIG. 6B illustrates an example of an antenna deviceincluding a ferrite sheet that is arranged so as not to overlap the feedcoil 10.

In the antenna device illustrated in FIG. 6A, there is not a ferritesheet between the coil antenna 20 and the ground conductor 52, and thusan eddy current flows through the ground conductor 52 due to theinduction magnetic field of the current flowing through the coil antenna20, and an eddy current loss occurs. Further, the coil antenna 20 isdirectly adjacent to the feed coil 10 and the degree of couplingtherebetween is high, but the resonance frequency of the coil antenna 20is separated from the resonance frequency of the feed coil 10 (resonancepoints are separated from each other), and accordingly a transmissionloss of signal energy increases.

In the antenna device illustrated in FIG. 6B, there is the ferrite sheet30 in a portion between the coil antenna 20 and the ground conductor 52,and thus the occurrence of an eddy current loss can be suppressed orprevented compared to the antenna device illustrated in FIG. 6A.However, the occurrence of an eddy current loss is inevitable in aportion that is not covered by the ferrite sheet 30. Also, like theantenna device illustrated in FIG. 6A, there is a problem of atransmission loss of signal energy caused by separate resonance points.

FIGS. 7A-7D are diagrams illustrating changes in resonance frequenciesof the coil antenna and the feed coil in the structure of the antennadevice 101 according to the first preferred embodiment in a case wherethe thickness of the ferrite sheet 30 is changed. The conditions underwhich the results illustrated in FIG. 7A to FIG. 7D are obtained are asfollows.

Ferrite Sheet {(A) to (D) Correspond to FIG. 7A to FIG. 7D}

(A) Real part permeability W=70, thickness δ=50 μm [the product ofrelative permeability of the magnetic material and the thickness (unitsof millimeters)=3.5]

(B) Real part permeability W=70, thickness δ=100 μm [the product ofrelative permeability of the magnetic material and the thickness (unitsof millimeters)=7]

(C) Real part permeability W=70, thickness δ=500 μm [the product ofrelative permeability of the magnetic material and the thickness (unitsof millimeters)=35]

(D) No ferrite sheet

Feed Coil

Inductance 0.74 μH

Coil Antenna

Planar dimension: 40 mm×40 mm

Thickness: 100 μm

RFID IC Chip

PN-544 manufactured by NXP Semiconductors

Reader/Writer

VIVO5000 manufactured by VIVOtech

In FIG. 7A to FIG. 7D, a curve s represents frequency characteristics ofthe feed coil 10 alone, and a curve d represents frequencycharacteristics in a state where the feed coil 10 and the coil antenna20 are coupled to each other. The frequency characteristics of the coilantenna 20 alone are equivalent to those represented by the curve s.

In the examples illustrated in FIG. 7A and FIG. 7B, the coupling betweenthe feed coil 10 and the coil antenna 20 breaks degeneracy and causesthe resonance points to be separated from each other, but the maximumcommunication distance is 37 mm. In contrast, in the example illustratedin FIG. 7C, the feed coil 10 and the coil antenna 20 are not coupled toeach other, and the maximum communication distance is only about 25 mm,for example. Also, as illustrated in FIG. 7D, in a case where no ferritesheet is provided, the coupling between the feed coil 10 and the coilantenna 20 significantly breaks degeneracy and causes the resonancepoints to be significantly separated from each other. Furthermore, aneddy current loss occurs in the ground conductor 52, and thus themaximum communication distance is about 20 mm, for example.

In the first preferred embodiment, as illustrated in FIG. 5B and soforth, the feed coil 10 and the coil antenna 20 are disposed such thatthe winding axis of the feed coil 10 is perpendicular or substantiallyperpendicular to the winding axis of the coil antenna 20, that the feedcoil 10 and the coil antenna 20 partially overlap each other in planview of the coil antenna 20, and that the opening portions (endportions) of the feed coil 10 protrude from the region where theconductors of the coil antenna 20 are provided. Accordingly, even if thedistance between the coil antenna 20 and the feed coil 10 is large, therelationship in which the magnetic flux φa is interlinked with the coilantenna 20 and the magnetic flux φb is interlinked with the feed coil 10is maintained, and stable communication characteristics are obtained.

As illustrated in FIG. 2A, the ground conductor (conductive layer) 52 isarranged so as to sandwich, with the coil antenna 20, the feed coil 10.The ground conductor 52 extends along the winding axis of the coilpattern 12 of the feed coil 10. The ground conductor 52 is disposed soas to cover the feed coil 10 and such that at least a portion of theground conductor 52 is positioned inside the inner peripheries of thecoil conductors of the coil antenna 20 in plan view. In FIG. 2A, W10represents the width of the feed coil 10, and D20 represents the innerperipheries of the coil conductors of the coil antenna 20.

With the above-described configuration, the magnetic flux generated bythe coil antenna 20 is along the ground conductor 52, and the magneticflux is easily interlinked with the feed coil 10. Thus, the existence ofthe ground conductor 52 increases the degree of coupling between thefeed coil 10 and the coil antenna 20. This configuration is effective inthe case of increasing the degree of coupling between the feed coil 10and the coil antenna 20 even if the size of the feed coil 10 isparticularly small, or if the distance between the feed coil 10 and thecoil antenna 20 is relatively large.

Second Preferred Embodiment

FIG. 8A is a schematic perspective view of an antenna device 102according to a second preferred embodiment of the present invention, andFIG. 8B is a front view of the antenna device 102. In the secondpreferred embodiment, the feed coil 10 is mounted on the printed wiringboard 50 such that the direction of the winding axis of the feed coil 10is the same as the direction of the winding axis of the coil antenna 20.The configuration of the antenna device 102 is the same as theconfiguration of the antenna device 101 according to the first preferredembodiment except that the mount position of the feed coil 10 isdifferent.

The antenna device 102 according to the second preferred embodiment iscapable of ensuring a communication distance that is equivalent orsubstantially equivalent to that of the antenna device 101 according tothe first preferred embodiment. However, if the distance between thefeed coil 10 and the coil antenna 20 increases, or the positionalrelationship therebetween changes, or if the resonance frequency of thecoil antenna 20 varies, the resonance frequency of the antenna device102 may fluctuate.

Third Preferred Embodiment

FIG. 9A is a schematic perspective view of an antenna device 103according to a third preferred embodiment of the present invention, andFIG. 9B is a partial plan view of the antenna device 103. FIG. 10A is aschematic cross-sectional view of a communication terminal apparatus 203including the antenna device 103. FIG. 10B is a plan view of the antennadevice 103 included in the communication terminal apparatus 203.

In the antenna device 103 and the communication terminal apparatus 203according to the third preferred embodiment, the coil antenna 20 isdisposed at or substantially at the center of the terminal housing 60when viewed from the back surface LF of the terminal housing 60. Thefeed coil 10 is disposed such that the coil opening surface thereof isclose to a side edge portion SE of the terminal housing 60. Accordingly,even if the coil antenna 20 is disposed at or substantially at thecenter of the terminal housing 60, the magnetic flux passing through thefeed coil 10 can be caused to go around in the direction of the sideedge portion SE of the terminal housing 60. That is, duringtransmission, the magnetic flux from the feed coil 10 goes around in thedirection of the side edge portion SE. During reception, the magneticflux from the communication partner is oriented in the direction of theside edge portion SE so as to mainly avoid the printed wiring board 50.Thus, for example, in a case where metal bodies such as variouselectronic components 71 and a battery pack 72 are disposed in thedirection perpendicular or substantially perpendicular to the directionof the side edge portion SE, collision of the magnetic flux passingthrough the feed coil 10 with the metal bodies is significantly reducedor prevented. Accordingly, a decrease in communication distance isprevented.

In the communication terminal apparatus 203, the various electroniccomponents 71, which constitute the communication terminal apparatus203, are mounted as surface mount components on the printed wiring board50 disposed in the terminal housing 60. Also, the battery pack 72 isdisposed near the coil antenna 20. On the second principal surface sideof the coil antenna 20, the ferrite sheet 30 is adhered to the entiresecond principal surface of the coil antenna 20. Thus, even if metalbodies other than the ground conductor 52 (for example, the variouselectronic components 71 and the battery pack 72) are disposed near thecoil antenna 20, an eddy current loss due to these metal bodies is lesslikely to occur. For a similar reason, the amount of variation of theresonance frequency of the coil antenna 20 is small.

Fourth Preferred Embodiment

FIG. 11A is a schematic perspective view of an antenna device 104according to a fourth preferred embodiment of the present invention, andFIG. 11B is a front view of the antenna device 104. In the antennadevice 104 according to the fourth preferred embodiment, the feed coil10 is disposed so as not to overlap the ferrite sheet 30 in plan view inthe direction of the winding axis of the coil antenna 20. Also in thiscase, the feed coil 10 is disposed on the opposite side of the coilantenna 20 with respect to the flat surface including the ferrite sheet30, so that the feed coil 10 and the coil antenna 20 are magneticallycoupled to each other via the ferrite sheet 30. That is, the feed coil10 and the coil antenna 20 are magnetically coupled to each other viathe magnetic flux that has been transmitted through the ferrite sheet30.

Fifth Preferred Embodiment

FIG. 12A is a schematic perspective view of an antenna device 105Aaccording to a fifth preferred embodiment of the present invention, FIG.12B is a schematic perspective view of an antenna device 105B accordingto the fifth preferred embodiment, and FIG. 12C is a partial plan viewof the antenna devices 105A and 105B. In the antenna devices 105A and105B according to the fifth preferred embodiment, in plan view in thedirection of the winding axis of the coil antenna 20, the feed coil 10is disposed at or substantially at the center of the coil opening of thecoil antenna 20. The feed coil 10 may be disposed such that the windingaxis of the feed coil 10 is perpendicular or substantially perpendicularto the winding axis of the coil conductors of the coil antenna 20, asillustrated in FIG. 12A, or may be disposed such that the winding axisof the feed coil 10 is parallel or substantially parallel with thewinding axis of the coil conductors of the coil antenna 20, and alsothat both the winding axes match each other, as illustrated in FIG. 12B.

Sixth Preferred Embodiment

FIG. 13 is a partial plan view of a communication terminal apparatus 206including an antenna device according to a sixth preferred embodiment ofthe present invention. In the communication terminal apparatus 206, thecoil antenna 20 and the ferrite sheet 30 are disposed so as not tooverlap a camera module 73 and a speaker 74.

In this way, it is not necessary that the outer shapes of the coilantenna 20 and the ferrite sheet 30 be rectangular or substantiallyrectangular. The coil antenna 20 and the ferrite sheet 30 may have arecessed portion or a protruded portion.

Seventh Preferred Embodiment

FIG. 14A is a schematic perspective view of an antenna device 107according to a seventh preferred embodiment of the present invention,and FIG. 14B is a front view of the antenna device 107. FIGS. 15A-15Care diagrams each illustrating the angle formed by a communicationterminal apparatus 207 including the antenna device 107 and a coilantenna on the communication partner side.

In the antenna device 107, as illustrated in FIG. 14A and FIG. 14B, thecoil antenna 20 is a planar coil including a first flat surface FS1 anda second flat surface FS2 that is connected to the first flat surfaceFS1. Also, the ferrite sheet 30 includes a first flat surface FS1 and asecond flat surface FS2, and is arranged so as to cover the coilconductors of the coil antenna 20 and the opening surface thereof. Thefeed coil 10 is disposed in a region surrounded by the first flatsurfaces FS1 and the second flat surfaces FS2 of the coil antenna 20 andthe ferrite sheet 30. The first flat surface FS1 is parallel orsubstantially parallel with the principal surface of the terminalhousing 60, and the second flat surface FS2 extends along the plane ofan end FE of the terminal housing 60 to form an angle with the firstflat surface FS1.

With this configuration, communication can be performed in any of thefollowing cases: a case where the principal surface of the terminalhousing 60 is parallel or substantially parallel with the coil openingsurface of a coil antenna 301 on the communication partner side, asillustrated in FIG. 15A; a case where the principal surface of theterminal housing 60 and the coil opening surface of the coil antenna 301on the communication partner side form an angle of approximately 45degrees, as illustrated in FIG. 15B; and a case where the principalsurface of the terminal housing 60 and the coil opening surface of thecoil antenna 301 on the communication partner side form an angle ofapproximately 90 degrees, as illustrated in FIG. 15C.

In this preferred embodiment, the angle formed between the first flatsurface FS1 and the second flat surface FS2 preferably is approximately90 degrees. Alternatively, the angle may be an obtuse angle of about 120degrees, or may be an acute angle of about 45 degrees, for example.Alternatively, instead of using a configuration in which the first flatsurface FS1 and the second flat surface FS2 are arranged with a certainangle formed therebetween, the first flat surface FS1 and the secondflat surface FS2 may be connected to each other via a curved surface, orthe portion corresponding to the first flat surface FS1 and the secondflat surface FS2 may be defined by a single curved surface.

Eighth Preferred Embodiment

FIG. 16A is a plan view of an antenna device 108 according to an eighthpreferred embodiment of the present invention, FIG. 16B is a partialplan view thereof, and FIG. 16C is a cross-sectional view taken along aC-C portion of FIG. 16B. In the antenna device 108, in plan view in thedirection of the winding axis of the coil conductors of the coil antenna20, the feed coil 10 is disposed outside the region where the coilconductors 22 (22 a and 22 b) of the coil antenna 20 are provided. Notethat an extended portion 22E is provided at a portion of outer edges ofthe coil conductors 22 (22 a and 22 b), and the feed coil 10 is disposedat a position that overlaps the extended portion 22E. Also, the ferritesheet 30 is extended so as to overlap the extended portion 22E.

In a case where the feed coil 10 is disposed outside the coil conductors22 (22 a and 22 b), the degree of coupling between the feed coil 10 andthe coil antenna 20 may become too small. It is preferable that, as inthis preferred embodiment, an extended portion be provided at a portionof the coil antenna 20 and a portion of the ferrite sheet 30 so as tooverlap the feed coil 10.

Ninth Preferred Embodiment

In a ninth preferred embodiment of the present invention, a descriptionwill be given of the relationship between the permeability and thicknessof a magnetic layer and the communication distance.

FIG. 17A is a diagram illustrating the induction magnetic field of theantenna device in a case where the permeability of the ferrite sheet 30(magnetic layer) is high, or in a case where the thickness of theferrite sheet 30 is large. FIG. 17B is a diagram illustrating theinduction magnetic field of the antenna device in a case where thepermeability of the ferrite sheet 30 (magnetic layer) is low, or in acase where the thickness of the ferrite sheet 30 is small.

In a case where the product of the relative permeability and thicknessof the ferrite sheet 30 (magnetic layer) is large, the degree ofmagnetic coupling between the magnetic flux φa from the communicationpartner and the coil antenna 20 is high, but the degree of magneticcoupling represented by the magnetic flux φb between the coil antenna 20and the feed coil 10 is low, as illustrated in FIG. 17A. As a result,the maximum communication distance is short.

In the opposite case, as illustrated in FIG. 17B, the degree of magneticcoupling represented by the magnetic flux φb between the feed coil 10and the coil antenna 20 is high, but the magnetic flux φa from thecommunication partner easily passes through the ferrite sheet 30 and iseasily coupled to the ground conductor 52. As a result, an eddy currentgenerated in the ground conductor 52 increases, and communicationcharacteristics degrade.

FIG. 18A is a diagram illustrating the relationship between the productof the relative permeability (real part permeability μ′) and thethickness of the ferrite sheet 30 and the maximum communicationdistance. FIG. 18B illustrates a table of the values thereof. Theconditions under which this result is obtained are as follows.

Coil Antenna

Outer shape 40 mm×40 mm

3 turns×both sides

Line width=1 mm

Distance between lines 1 mm

Ferrite Sheet

The size is the same as that of the outer shape of the coil antenna

Card of Communication Partner

A typical card of the ISO 14443A standard (a size of about 80 mm×50 mm)

As illustrated in FIG. 18A and FIG. 18B, in a case where the product ofthe relative permeability and the thickness of the ferrite sheet 30 isless than 20, a maximum communication distance of about 30 mm isensured. In a case where the maximum communication distance is about 30mm or more, stable communication can be performed even in a case wherethe antenna device is disposed in the terminal housing and communicationis performed via the thickness of the terminal housing, or in a casewhere a certain gap exists between the antenna device and thecommunication partner.

Tenth Preferred Embodiment

In a tenth preferred embodiment of the present invention, a descriptionwill be given of optimization of the pattern of coil conductors of thecoil antenna. FIG. 19A is a perspective view of the coil antenna 20, andFIG. 19B is an exploded perspective view of the coil antenna 20. FIG.20A is a plan view of the coil antenna 20, and FIG. 20B is an equivalentcircuit diagram of the coil antenna 20.

In the coil antenna 20, the first coil conductor 22 a is located on thefirst principal surface (upper surface) of the base sheet 21, which ispreferably made of PET or the like, and the second coil conductor 22 bis provided on the second principal surface (lower surface). The windingdirection of the first coil conductor 22 a and the winding direction ofthe second coil conductor 22 b are opposite to each other (the same inperspective view). The equivalent circuit thereof is illustrated in FIG.20B.

Referring to FIG. 20B, inductors L1 and L2 correspond to the coilconductors 22 a and 22 b. A capacitor C1 corresponds to a capacitancethat is generated mainly at the vicinities of outer ends of the coilconductors 22 a and 22 b, and a capacitor C2 corresponds to acapacitance that is generated mainly at the vicinities of inner ends ofthe coil conductors 22 a and 22 b. Here, in a case where design isperformed so that C1>>C2≈0 is satisfied by increasing the area in whichthe vicinities of the outer ends of the coil conductors 22 a and 22 bface each other and decreasing the area in which the vicinities of theinner ends of the coil conductors 22 a and 22 b face each other, theportion of the capacitor C2 is substantially in an open state, and acurrent hardly flows to an electrode near the capacitor C2. That is, theelectric field becomes maximum. In contrast, an electrode near thecapacitor C1 that is the farthest from the electrode near the capacitorC2 is a maximum current point. That is, the amount of current flowingthrough the coil conductors 22 a and 22 b is large on the outer side andsmall on the inner side.

As a result, a region where a magnetic field is generated is theoutermost side of the coil antenna 20. This means that the equivalentantenna size is large, and thus an antenna with favorable radiationefficiency can be obtained.

Eleventh Preferred Embodiment

In an eleventh preferred embodiment of the present invention, adescription will be given of other two patterns of the coil conductorsof the coil antenna. FIG. 21A and FIG. 21B are plan views of a coilantenna. In either example, the capacitance is larger on the outer sideof the coil conductors 22 a and 22 b, and the capacitance is smaller onthe inner side.

In the example in FIG. 21A, the capacitance is adjusted by changing theline width of a coil conductor. Specifically, the line width of the coilconductor 22 a is constant, whereas the line width of the coil conductor22 b decreases from the outer side toward the inner side. In the examplein FIG. 21B, the line width of a portion in which the coil conductors 22a and 22 b face each other decreases from the outer side toward theinner side (the amount of positional deviation increases).

Twelfth Preferred Embodiment

In a twelfth preferred embodiment of the present invention, adescription will be given of the relationship between the maximumcommunication distance and the positional relationship between one endof the feed coil 10 and the ferrite sheet 30.

FIG. 22A includes a plan view and a front view of the antenna device,and FIG. 22B is a diagram illustrating the relationship between themaximum communication distance and a dimension Y from an end portion ofthe ferrite sheet 30 to one end of the feed coil 10. The conditionsunder which this result is obtained are as follows.

Coil Antenna

Planar dimension: 40 mm×40 mm

Thickness: 50 μm

6 turns×both sides

Line width=1 mm

Distance between lines=0.5 mm

Ferrite Sheet

Planar dimension: 40 mm×40 mm

Thickness: 100 μm

Relative permeability: about 130

[Printed Wiring Board]

Planar dimension: 50 mm×110 mm

Feed Coil

Planar dimension: 5 mm×5 mm

Thickness: 0.8 μm

Distance Between Ferrite Sheet and Printed Wiring Board

1.2 mm

As illustrated in FIG. 22B, in a case where the dimension Y from the endportion of the ferrite sheet 30 to one end of the feed coil 10 is 0 mmor about 35 mm to about 40 mm, for example, the most favorablecharacteristics are obtained.

A state where Y=0 mm or 35 mm is a state where one end of the feed coil10 is in contact with the end portion of the ferrite sheet 30. A statewhere Y=40 mm is a state where the other end of the feed coil 10 is incontact with the end portion of the ferrite sheet 30.

FIGS. 23A and 23B are front views of the antenna device. As illustratedin FIG. 23A, in a case where the opening portion of the feed coil 10protrudes from the outer shape of the coil antenna 20, the magnetic fluxfrom the feed coil 10 goes around on the outer side of the coil antenna20, and is interlinked with the opening portion of the coil antenna 20.Accordingly, the feed coil 10 and the coil antenna 20 are coupled toeach other more strongly. On the other hand, in a case where the openingportion of the feed coil 10 does not protrude from the outer shape ofthe coil antenna 20, as illustrated in FIG. 23B, the magnetic flux fromthe feed coil 10 is not interlinked with the opening portion of the coilantenna 20 due to an influence of the ferrite sheet 30. Therefore, thedegree of coupling between the feed coil 10 and the coil antenna 20 isslightly lower than the above-descried case.

In this way, the feed coil 10 and the coil antenna 20 are disposed suchthat the feed coil 10 and the coil antenna 20 partially overlap eachother and that the opening portion (end portion) of the feed coil 10protrudes from the outer shape of the coil antenna 20 in plan view ofthe coil antenna 20. Accordingly, the degree of coupling between thefeed coil 10 and the coil antenna 20 increases, and stable communicationcharacteristics can be obtained even if the distance between the coilantenna 20 and the feed coil 10 increases.

In the above-described preferred embodiments, a description has beenmainly given of examples in which the “conductive layer” is a groundconductor of a printed wiring board. Alternatively, a conductive platesuch as a liquid crystal panel, a battery pack, or a shield case may beused as the “conductive layer”, for example.

As described above, preferred embodiments of the present invention canbe utilized for antenna devices and communication terminal apparatuses,in particular, an antenna device used for an RFID tag or a reader/writerthat operates in an HF band, and a communication terminal apparatusincluding the antenna device. Preferred embodiments of the presentinvention are useful for an RFID system or the like for performingbilling or article management.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. (canceled)
 2. An antenna device comprising: a feed coil connected toa feed circuit; a coil antenna disposed near the feed coil; and amagnetic layer provided between the feed coil and the coil antenna;wherein a product of a relative permeability of a magnetic material ofthe magnetic layer and a thickness of the magnetic layer is less thantwenty; and the feed coil and the coil antenna are magnetically coupledto each other via the magnetic layer.
 3. The antenna device according toclaim 2, wherein the coil antenna is a planar coil that includes a firstprincipal surface and a second principal surface, the first principalsurface is oriented toward an antenna on a communication partner side,the second principal surface is opposite to the first principal surface,and the magnetic layer is arranged so as to cover the second principalsurface of the coil antenna.
 4. The antenna device according to claim 3,wherein the coil antenna includes a first coil conductor that is planarand is located on the first principal surface, and a second coilconductor that is planar and is located on the second principal surface;an inductance of the first coil conductor, an inductance of the secondcoil conductor, and a capacitance generated between the first coilconductor and the second coil conductor define an LC parallel resonancecircuit; and an area in which the first coil conductor and the secondcoil conductor face each other in plan view of the coil antenna islargest near outer end portions of the first coil conductor and thesecond coil conductor and is smallest at inner end portions of the firstcoil conductor and the second coil conductor.
 5. The antenna deviceaccording to claim 3, wherein the antenna device includes a conductivelayer, and the magnetic layer is provided between the second principalsurface of the coil antenna and the conductive layer.
 6. The antennadevice according to claim 2, wherein the feed coil is disposed such thatat least a portion of the feed coil overlaps the magnetic layer in planview of the coil antenna.
 7. The antenna device according to claim 2,wherein the feed coil is disposed such that a winding axis of the feedcoil is perpendicular or substantially perpendicular to a winding axisof the coil antenna.
 8. The antenna device according to claim 2, whereinthe coil antenna is a resonance circuit that has a resonance frequencycorresponding or substantially corresponding to a carrier frequency of acommunication signal.
 9. The antenna device according to claim 2,wherein the feed coil and the feed circuit define a resonance circuitthat resonates at a frequency corresponding to a carrier frequency of acommunication signal.
 10. The antenna device according to claim 2,wherein the coil antenna is a planar coil that includes at least a firstflat surface and a second flat surface which is connected to the firstflat surface, and the feed coil is disposed in a region surrounded bythe first flat surface and the second flat surface.
 11. The antennadevice according to claim 2, wherein the magnetic layer has a thicknessof about 300 μm or less.
 12. A communication terminal apparatuscomprising: a housing; a feed circuit provided in the housing; a feedcoil connected to the feed circuit; a coil antenna disposed near thefeed coil; and a magnetic layer provided between the feed coil and thecoil antenna; wherein the feed coil and the coil antenna areelectromagnetically coupled to each other via the magnetic layer. 13.The communication terminal apparatus according to claim 12, wherein thefeed coil is disposed in the housing near an end portion of the housingsuch that a winding axis of the feed coil is perpendicular orsubstantially perpendicular to an end surface of the housing.
 14. Thecommunication terminal apparatus according to claim 12, wherein the coilantenna is a planar coil that includes at least a first flat surface anda second flat surface which is connected to the first flat surface, thefirst flat surface is parallel or substantially parallel with aprincipal surface of the housing, and the second flat surface extendsalong an end portion of the housing to form an angle with the first flatsurface.
 15. The communication terminal apparatus according to claim 12,further comprising a conductive layer that extends along a winding axisof the feed coil such that the feed coil is sandwiched between theconductive layer and the coil antenna, the conductive layer is disposedsuch that, in plan view, the conductive layer covers the feed coil andat least a portion of the conductive layer is positioned inside an innerperiphery of a coil conductor of the coil antenna.
 16. The communicationterminal apparatus according to claim 12, wherein a product of arelative permeability of a magnetic material of the magnetic layer and athickness of the magnetic layer is less than twenty.
 17. Thecommunication terminal apparatus according to claim 12, wherein the feedcoil is disposed such that at least a portion of the feed coil overlapsthe magnetic layer in plan view of the coil antenna.
 18. Thecommunication terminal apparatus according to claim 12, wherein the coilantenna is a resonance circuit that has a resonance frequencycorresponding or substantially corresponding to a carrier frequency of acommunication signal.
 19. The communication terminal apparatus accordingto claim 12, wherein the feed coil and the feed circuit define aresonance circuit that resonates at a frequency corresponding to acarrier frequency of a communication signal.
 20. The communicationterminal apparatus according to claim 12, wherein the coil antenna is aplanar coil that includes at least a first flat surface and a secondflat surface which is connected to the first flat surface, and the feedcoil is disposed in a region surrounded by the first flat surface andthe second flat surface.
 21. The communication terminal apparatusaccording to claim 12, wherein the magnetic layer has a thickness ofabout 300 μm or less.